The embodiments of the invention relate to a method for inspecting a valve drive, in particular for ascertaining a valve position of a valve of an internal combustion engine, and to a corresponding device.
During the production of internal combustion engines, it is necessary for the assembled engine (entire engine) to be subjected to a function test in order to inspect a valve drive, in particular the opening and closing times of the inlet and outlet valves, and measure the control timing. Here, the internal combustion engine is subjected, for example, to the so-called “cold test”, in which the internal combustion engine is driven by way of a cranking drive. Alternatively, control timing measurement devices are known which operate by way of tactile measurement.
Both measurement methods necessitate the use of corresponding devices. These are however normally very large and expensive and require regular calibration. In particular in the case of very narrow cylinder heads, the use of the control timing measurement device is possible only with difficulty owing to the tactile measurement on the entire engine.
DE 10 2005 004 248 A1 has therefore disclosed an optical measurement method for the ascertainment, on an internal combustion engine, of the valve drive or of the position of a valve, by virtue of light being supplied to the respective valve from a side pointing toward the valve shank. In the combustion chamber there is arranged a light-sensitive measurement element which is capable of detecting a passage of light from the combustion chamber upon opening of the valves and an obstruction of light upon closing of the valves.
Said optical method has the characteristic that, in the case of an internal combustion engine having multiple valves per combustion chamber, only the opening of the first valve can be detected. As soon as the first valve is opened, light passes via the opened valve into the combustion chamber and is detected there. If a second valve opens while the first valve is still open, then it is the case that, in addition to the light entering via the first valve, light also passes into the already illuminated combustion chamber via the second valve. The measurement element arranged there thus cannot detect a change. Consequently, the method permits only the detection of the first entry of light after the opening of the first valve, such that an opening time of the second valve therefore cannot be determined.
It is thus an object of the embodiments of the invention to make it possible for opening and closing times of individual valves to be detectable independently of one another.
Said object is achieved by way of the method as per claim 1 or 2, and by way of a device having the features of patent claim 7.
Advantageous embodiments emerge from the respectively dependent patent claims.
Accordingly, a method for ascertaining a valve position of a valve of an internal combustion engine having a multiplicity of valves is provided, having the following steps:                illuminating a combustion chamber of the internal combustion engine,        detecting light emerging from the illuminated combustion chamber on a side, averted from the combustion chamber, of the valve for ascertainment,        determining the valve position of the valve for ascertainment by way of the detected light.        
The method is preferably utilized for ascertaining a respective valve position of at least two valves of an internal combustion engine having a multiplicity of valves, giving rise to the following steps:                illuminating a combustion chamber of the internal combustion engine,        detecting light emerging from the illuminated combustion chamber on a side, in each case averted from the combustion chamber, of the valves for ascertainment,        determining the respective valve position of the at least two valves for ascertainment on the basis of the light detected in each case.        
In each case, therefore, the combustion chamber of the internal combustion engine is illuminated by way of a light source. For as long as the valve for ascertainment is closed, no light passes out of the combustion chamber through the valve. The closed position of the valve can thus be uniquely identified. As soon as the valve then opens, light passes out of the combustion chamber and can be detected on that side of the valve which is averted from the combustion chamber. This makes it possible for the present position of the valve to be determined in a particularly precise manner.
Here, a position of the other valves has no influence, such that the positions of more than one valve can also be determined independently of one another. In each case, light emerging from the combustion chamber is detected on the valve side averted from the combustion temperature in each case only when the associated valve is actually open. The position of the one or more other valves therefore does not influence the measurement, such that, for the individual determination of the respective valve position, it makes no difference whether the other valves are open or closed. In summary, the method according to the embodiments of the invention makes it possible for each valve position to be determined separately.
Furthermore, the step of detecting the emerging light may be performed continuously or discontinuously. This means that the detection of the light includes a continuous measurement of a light intensity, and thus any change can be immediately converted into a corresponding signal for a suitable further processing. In the case of a discontinuous detection, a measurement is performed only at defined points in time or at defined time intervals.
The step of detecting the emerging light thus preferably includes a detection of the change in light intensity and/or of a (complete) obstruction of the light emerging from the combustion chamber. The obstruction of the detected light unequivocally indicates that the valve is situated in the closed position, and a sealing action is realized.
The measurement of the light intensity may be utilized to make a distinction between the closed position and the open position. In addition, a distinction may be made between intermediate values for the values of the light intensity arising between the closed position and the open position, in order thereby to ascertain one or more intermediate positions of the valve.
In one embodiment, each valve is assigned a respective light sensor, and the method furthermore includes a step of assigning the light detected by way of the at least one light sensor to the respective valve assigned to the light sensor.
This makes it possible to uniquely ascertain an individual position of each of the valves for measurement. This is realized in that the light from the combustion chamber can pass to the respective light sensor only when the associated valve is actually open. An influence arising from an opening or closing of another valve is thus prevented in an effective manner at all times.
Furthermore, the method may also include a step of detecting a crank angle of a crankshaft of the internal combustion engine.
The information regarding the crank angle may be used to assign the detected valve position to the associated rotational position of the engine.
For the implementation of the method, the internal combustion engine may furthermore be driven with cranking action by way of a separate drive. This may for example be performed before or during the so-called cold test.
By way of the described method, it is thus possible, given a known cam lift curve, for the control timing and a valve play to be tested on a valve-specific basis on the assembled entire engine.
Also described is a device for ascertaining a valve position of at least one valve of an internal combustion engine, having a combustion chamber of the internal combustion engine, and having a light source and at least one light sensor for detecting the light of the light source, characterized in that the light source is designed to illuminate the combustion chamber, and the at least one light sensor is designed to detect the light emerging from the illuminated combustion chamber on a side, averted from the combustion chamber, of the at least one valve.
For example, the light source includes an illuminant, in particular an incandescent lamp, an LED illuminant or a laser. The light source is for example installed in place of the spark plug or glow plug in order to illuminate the interior of the combustion chamber.
The at least one light sensor is preferably arranged on that side of the at least one valve which is averted from the combustion chamber, in particular in an inlet or outlet duct assigned to the at least one valve.
This means that the light sensor either may be arranged within the inlet or outlet ducts, or is arranged such that said light sensor can at least detect the light intensity within the inlet or outlet duct. For example, the light sensor may issue into the respective duct for this purpose.
Alternatively, the arrangement includes a multiplicity of light sensors, wherein each light sensor is assigned to a respective arm of a split inlet or outlet duct.
Furthermore, the arrangement can include a cranking drive for driving the internal combustion engine with cranking action.
Other objects, advantages and novel features of the embodiments of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings, in which: